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Sample Comparison of Surface Observatons and UV Index Forecasts

A good example of how well the UV Index forecasts and observations agree is shown in Figure 5.

Figure 5

This figure shows how the forecasts and observations are compared "by eye". Besides the observations and the UV Index forecasts, the "clear sky" UV Index forecasts are also shown. This provides a indicator of the maximum values at each particular site. The only factors affecting this value is the solar zenith angle and the total ozone amount. Note that the day-to-day variation of total ozone does introduce variations in the clear sky amounts. Note also, the number of occasions when overcast conditions occur and the large differences between observed and forecast UV Index amounts. As explained above, the large differences that occur when overcast conditions exist show up on the negative side of the histograms.

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